1. Field of the Invention
The present invention relates to seat belt systems designed to protect the occupants of a vehicle during a collision. More specifically, the invention relates to an electric seat belt retractor system which is uniquely capable of protecting an occupant during normal use, pre-crash situations, and crash situations, and is capable of constantly and dynamically adjusting to the positioning of the occupant.
2. Description of Related Art
A “control system” may be defined as a system in which an operation is to be performed (or omitted) in a manner determined by measuring some characteristic of the system. Thus, efficient operation of the system can be maintained despite relatively unpredictable changes in the system. The present invention has application to a wide variety of control systems.
There are many applications in which it may be desirable to monitor and/or automatically adjust the tension in a flexible member. One such application is safety restraints for protecting vehicle occupants from impact. Such restraints are often known as “seat belts.”
Seat belts are known to increase the safety of occupants in motorized vehicles. Seat belt use is often cited as the most useful line of defense in reducing accident related injuries. Legislation requiring manufacturers to include seat belts in their vehicles has been in place for many years. More recently, laws have been enacted requiring consumers to use seat belts.
The benefits of seat belt use are numerous. In a collision, seat belts may prevent the occupant of a vehicle from striking the interior of the vehicle or other objects within the vehicle, including other occupants. Seat belts aid in keeping the occupant inside the vehicle during a roll-over or other accident situation to enhance the probability of survival and injury avoidance. Seat belts may also keep the driver behind the wheel and in control of the vehicle prior to an impending or potential collision, averting additional damage or injuries. Seat belts also enhance the effectiveness of other safety devices. For example, in a vehicle with airbags, a seat belt keeps the occupant in the seat so that the airbag can better protect the occupant.
Seat belts vary in their configuration, but one common type of seat belt is the three point safety harness. A three point safety harness includes a lap belt and a shoulder strap that cooperate to anchor an occupant on each side of his/her lap and at one shoulder. In one commonly employed three-point safety harness configuration, the seat belt webbing traverses the occupant's upper body in a diagonal fashion, passes through a latch plate, and then traverses the occupant's lap. The latch plate is fastened to a buckle, which is secured to the vehicle to restrain both the occupant's lower and upper body. One end of the webbing is typically anchored to the vehicle. The other end is secured by a seat belt retractor.
For convenience and due to variations in seat position and occupant size, three point safety harnesses are usually adjustable to provide proper safety and comfort. A seat belt retractor allows the safety harness to be adjustable and to lock the webbing in the event of an accident. Conventional seat belt retractors include webbing anchored at one end to a spool. Rotation of the spool is controlled for extraction and retraction of the webbing by a combination of various ratchet wheels, springs, lock dogs, pawls, gears, and the like.
Preferably, in a three-point safety harness, the shoulder strap rests lightly on the occupant's shoulder and allows the occupant's upper torso relatively free movement. However, many occupants fail to properly adjust the tension in the safety harness once the seat belt has been fastened. If too much slack is left in the shoulder strap portion of the webbing, the shoulder seat belt system may not properly protect the occupant. Therefore, seat belt retractors have been designed to automatically remove excess slack from the shoulder strap. Generally, this is done by providing a constant bias on the spool in the direction of webbing retraction. However, in actual application, seat belt systems usually contain substantial slack, often 120 mm or more. This is clearly not ideal in that the slack can defeat the effectiveness of the seat belt in a crash situation.
In addition, removal of slack can often cause the occupant discomfort. This discomfort may cause an occupant to use the seat belt improperly, for example, by placing the shoulder portion behind their upper torso, or by simply not using the seat belt. The safety features of the three-point safety harness are defeated when discomfort leads occupants to misuse or avoid using the system.
Generally, the difficulty with existing seat belt systems can be summarized as inability to adequately and dynamically adjust to the position of the occupant. An ideal seat belt system should be able to restrain an occupant comfortably during normal operation. This, however, requires constant adjustment because the occupant is constantly mobile, moving and reaching about the interior of the vehicle. Conventional systems are unable to freely and constantly adjust and often result in uncomfortable binding if the occupant makes a substantial move.
Furthermore, most conventional systems are unable to adequately respond to pre-crash situations. Most existing systems simply lock the belt in place, but are unable to draw the occupant back into position. Many such systems are unable to provide crash pretensioning to restrain the occupant during an actual crash, and to allow optimum interaction with airbags and other supplemental restraint systems.
Hence, conventional seat belt systems are lacking in a number of respects, and a need exists for enhanced seat belt systems that overcome the shortcomings of the prior art. More generally, there is a need for control systems capable of adjusting the available length of a flexible member depending on tension present within the member. Conventional control systems generally lack the ability to dynamically and accurately control the tension. There is a need for control systems capable of controlling tension, particularly in the presence of relatively unpredictable factors such as the motion of a vehicle passenger.